Amongst the numerous methods of modifying the surface state of materials such as paper or card for the purpose of printing thereon, proposals have already been made, e.g. in French patent specification No. FR-A-2 543 060, to apply a plurality of offset, silk-screen, or letterpress inks or varnishes having different polymerization temperatures and speeds, to perform pre-drying at an appropriate temperature and for a sufficient length of time to polymerize a certain type of ink and then to apply dusting particles to the treated surface, with the particles adherring solely to those inks which have not yet polymerized, and then to perform drying at an appropriate temperature and for an appropriate length of time to complete the polymerization of all the types of ink after removing excess dusting particles by suction and/or by blowing.
Although such a method gives satisfaction with dusting powders such as metal powders, asbestos powder, cork powder, etc. . . . , a number of precautions need to be taken when said dusting powders are based on thermoplastic or hot-setting materials which are caused to melt by appropriate heating means, in particular if the method is intended to be applied to treating surfaces which are very wide, or to certain types of special materials.
Although implementing the method of the above-mentioned French patent gives excellent results even when using powders of thermoplastic or hot-setting materials, for producing articles such as greetings cards, advertising sheets, magazine covers, etc., when the method is performed on media of larger sizes, the dusting treatment and in particular the time it takes causes the cost of articles manufactured in this way to become prohibitive, industrially.
Consequently, an object of the invention is to provide improvements to the above-outlined method which make it economically advantageous to perform the method regardless of the type of surface to be treated, and in particular on surfaces of great width, in the form of large sheets or in the form of reels.
Another object of the invention is to provide an installation for implementing the improved method, and in particular such an installation for printing on paper or card and suitable for treating sheets or reels having a width of 1020 mm to up to 1600 mm at a high or a very high rate.